Pollution Controls for a Chem-film Line

Posted on:7/1/2005

Question:
What is the set up for proper pollution controls on a chem-film line that is using well water, not city water and discharging to lagoon system.

Question:

What is the set up for proper pollution controls on a chem-film line that is using well water, not city water and discharging to lagoon system. What kind of system would I need? R.B.

Answer:

For such a short question, I could write many pages in reply. First, let's discuss the water supply. Since you will be using well water, it will likely be high in hardness and minerals and require treatment in order to be acceptable for your process line. The two most common technologies used for treatment of water for a metal finishing line are ion exchange and membrane filtration. Unless you use ion exchange canisters that are regenerated off-site by a service firm, I would lean toward membrane filtration due to the generation of regenerant acid and caustic wastes and your direct wastewater discharge.

Membrane filtration works best if the water is filtered upstream. Most installations use cartridge filters and others use microfiltration, but if your flow is high enough, using two continuous backwash sand filters in series could provide the needed feedwater quality at lower operating costs. Working with your chemical supplier and water system supplier, you can determine the level of treatment in order to produce the desired quality of water.

Since you are planning to use well water instead of city water, I assume that city water is not available. If the well water system is to provide drinking water to more than 25 people, four hours per day, four days per week and six months per year, it will be classified as a Non-Transient Non-Community public water system and is regulated by USEPA regulations 40CFR141 as well as your state EPA and/or state Health Department. These requirements can include, but not limited to, water quality assessment, system approval by state, well identification and registration, periodic and frequent water quality monitoring and analysis, licensed system operator, copper control, "public" notification, record keeping and reporting. Even if you do not meet the above criteria, many states regulate the supply of drinking water at some level, and let us not forget the liability you take on by producing drinking water. In order to have these drinking water regulations not apply, you could supply bottled drinking water and prominently label sink and hose faucets as "non-potable water, do not drink" or other similar scary language. You should still periodically test the water for bacteria since there is likely incidental contact with operators' skin at the process line.Since you also mentioned a "lagoon system," my assumption is that you will have a direct discharge. It is not possible to define what kind of wastewater treatment you will need without knowing what the likely discharge limitations will be. While one can start with USEPA Metal Finishing Point Source Category, New Source Performance Standards, 40CFR433.16 as a starting point, our experience has been that direct discharge limits are significantly less than those listed in these regulations. This is due to water quality standards of the receiving stream as well as biomonitoring, that is testing your wastewater using "baby" water flies, minnows or some other water species. Even though they consistently met their zinc numerical limit, one of our clients had to change their treatment process to significantly reduce zinc in the effluent in order to pass their biomonitoring test. Also, there are other pollutants regulated by the states that are not covered by USEPA's metal finishing regulations. Several common pollutants are total solids, chemical oxygen demand, phosphorus, ammonia, nitrates, nitrites, temperature, color, total residual chlorine, sulfates and sulfides. It is strongly recommended that you personnally meet with your direct discharge permit writer very early in the design process in order to determine likely discharge limits since there are so many variables that can make a significant impact, including flow rate, stream flow rate and type of stream. A small flow into a large river will have higher limits, maybe even much higher limits, than a small flow into a trout stream.

Next, I am very "nervous" about a "lagoon system." Due to the presence of heavy metal, acids and caustics, the design and installation of a lagoon system is highly regulated. Assuming that your state would approve such a system, it would likely require at least two synthetic liners with leak detection between liners and if the primary liner begins to leak, your lagoon would have to be emptied in order for the leak to be found and repaired.

Of course, you could always install two lagoon systems in parallel with its increased cost. Instead, I would recommend that the wastewaters be collected in lined, concrete sumps and pumped to an above ground wastewater treatment system which would have the proper corrosion protection and containment.

As far as treatment chemistries and technologies, you have many to choose from, but, until you know your target, they are not worthwhile to pursue aggressively. It is my opinion that the wastewater will likely require some type of filtration, maybe even membrane filtration such as microfiltration, in order to consistently produce a compliant wastewater. There are a number of reputable suppliers listed in the 2005 Directory and Technology Guide under the Pollution Control Chemicals and Pollution Control Equipment categories.

Instead of a direct discharge, I would also seriously evaluate the economic feasibility of no wastewater discharge by aggressively implementing rinsewater reduction, dragout recovery and water reuse techniques and technologies as well as concentrating contaminants for off-site treatment, disposal or reuse. The proven technologies are here; the only question is whether or not they are less costly than treatment for direct discharge. As compared to direct discharge, no discharge has a good chance to be least costly. For a description of the recovery techniques and technologies available, you can read "Recovery/Recycling Methods for Platers" in Product Finishing's 2005 Directory and Technology Guide ; it is authored by yours truly.

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